1. Field of the Invention
This invention relates to the field of phase demodulators and particularly to phase demodulators capable of demodulating with good linearity a signal, the phase of which is varied over a wide angle.
2. The Prior Art
One type of phase demodulators used heretofore has included a balanced circuit with two sets of input terminals, one to receive the modulated signal, and the other to receive a reference carrier signal. These signals are so related that when the modulation of the phase modulated signal is zero, the phase angle of that signal will be out of phase with respect to the reference carrier by a certain angle .theta.. When these two signals are combined, the resulting signal has certain overlap and may be represented by a pulse signal having a certain duty cycle. Phase modulation of the signal to be demodulated increases or decreases the overlap and thus, in effect, changes the duty cycle. This change in the duty cycle can be translated into a change in amplitude to complete the demodulation.
If the phase modulation is centered about a certain phase which differs by 90.degree. from the phase of the reference carrier, the duty cycle of the overlap signal will be 50 percent for the unmodulated signal, and will increase up to 100 percent when the modulation angle is .pi./2 and down to 0 percent when the modulation angle is - .pi./2. The average value of the overlap signal thus has a peak value for a modulation angle of .pi./2, and a peak value of the opposite polarity for a modulation angle of - .pi./2. Extending the modulation angle beyond these limits, reduces the average value, which is undesirable. At modulation angles of .+-. .pi. the average value is zero.
It is an object of the present invention to provide a phase demodulator having a wide demodulation range.
A further object of the present invention is to provide a phase demodulator that has good linearity.
A still further object of the present invention is to provide a phase demodulator capable of providing linear demodulation of signals having modulation angles that extend negatively beyond - .pi./2 and positively beyond + .pi./2.
Further objects will be apparent from the following specification together with the drawings.